Re: [Qemu-devel] Use of flash for x86 BIOS

[Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>]

On 04/08/2013 04:43 PM, Gleb Natapov wrote:
> On Mon, Apr 08, 2013 at 01:18:10AM -0700, Jordan Justen wrote:
>> On Sun, Apr 7, 2013 at 11:06 PM, Xiao Guangrong
>> <xiaoguangrong@linux.vnet.ibm.com> wrote:
>>> On 03/23/2013 03:09 AM, Jordan Justen wrote:
>>>
>>>> Admittedly, I've been completely ineffectual in resolving the kvm
>>>> portion. More recently I tried to make use of KVM_MEM_READONLY to
>>>> address this. I was able to get an VM exit on writes to flash, but not
>>>> able to get the memory region to convert to full device mode so VM
>>>> exits would occur on reads as well. I am once again stalled...
>>>
>>> Hi Jordan,
>>>
>>> What's memory region you want to get? I should admit that I do not
>>> have enough background of flash, could you please explain this
>>> requirement more detail?
>>
>> The flash memory requires two modes.
>>
>> Read/Execute mode:
>> * Initial state
>> * Writes will trap to QEMU, and may transition to Device mode based on
>> QEMU device emulation
>>
>> Device mode:
>> * Region is not executable
>> * All reads & writes will trap to QEMU
>> * May transition back to Read/Execute mode based on QEMU device emulation
>>
>> Using KVM_MEM_READONLY I was able to get Read/Execute mode to work,
>> but I was not able to get the memory region to transition to Device
>> mode. (I couldn't get reads to trap to QEMU.)
>>
> You need to drop memslot when you transition to Device mode.

Yes. After delete the memslot, you can intercept both write and read. ;)